In recent science and technology, electricity is used for everything such as electric power as a power source or electric signals, etc., and conductors such as cables or lead wires are used for transmission thereof. Metals having high conductivity such as copper or silver are used as a material of such conductors, and particularly, copper wires are used very often in view of the cost.
Although it is generically called “copper”, it is broadly classified into hard copper and soft copper depending on a molecular arrangement thereof. Then, copper having desired properties is used depending on the intended use.
A hard copper wire is often used for a lead wire for electronic component but a rigid hard copper wire is unsuitable for, e.g., a cable used in electronic devices, etc., such as medical equipment, industrial robot or notebook computer since it is used in an environment in which a combined external force of extreme bending, torsion and tension, etc., is repeatedly applied, and a soft copper wire is therefore used instead.
A conductor used for such an application is required to have conflicting characteristics, which are good conductivity (high conductivity) and good bending characteristics, and a copper material maintaining high conductivity and flexibility has been thus developed to date (see Patent Literature 1 and Patent Literature 2).
For example, the invention according to Patent Literature 1 is the invention relating to a flexible cable conductor with good tensile strength, elongation and conductivity, and particularly, a flexible cable conductor is described in which a wire rod is formed of a copper alloy made of oxygen-free copper with a purity of not less than 99.99 wt % containing indium with a purity of not less than 99.99 wt % at 0.05 to 0.70 mass % and P with a purity of not less than 99.9 wt % at a concentration range of 0.0001 to 0.003 mass %.
Meanwhile, the invention according to Patent Literature 2 describes a flexible copper alloy wire containing 0.1 to 1.0 wt % of indium, 0.01 to 0.1 wt % of boron and copper as the remainder.